(ISTANBUL) - A summit of Islamic countries in Istanbul next week will boost Turkey's quest to deepen ties with the Muslim world, but some of its new friends are not to the taste of its traditional ally, Washington.

Sudan's President Omar Hassan al-Bashir, who has an international arrest warrant against him for war crimes, and Iran's Mahmoud Ahmadinejad, engaged in a standoff with the West over Tehran's nuclear programme, are among leaders who will attend an Organisation of the Islamic Conference (OIC) meeting.

The one-day summit on Monday will add to growing concerns in some Western circles that Turkey, an OIC member which is seeking European Union membership, is shifting away from its pro-Western foreign policy and embracing countries such as Iran and Syria, while distancing itself from regional friend Israel.

"I think this summit will put Turkey again on the frontline, both in regards with Iran and Bashir," said Hugh Pope, a senior analyst for the International Crisis Group.

"Engagement and cooperation can be a way to bring autocratic states into the international system, but the challenge for Turkey is that it needs to show results and that the behaviour of these states is changing," Pope said.

Although the 57-nation body's meeting has been billed as an economic summit to discuss trade and anti-poverty measures among members, the presence of Bashir and Ahmadinejad will likely overshadow its economic goals.

Western powers are seeking to exert pressure on Tehran for concessions on its nuclear programme, and Ahmadinejad could use the summit to undermine efforts to isolate the Islamic republic and to give one of his trademark anti-Western speeches.

The West fears Tehran's nuclear programme is a covert plan to develop nuclear weapons, but Iran has denied this and says it needs nuclear technology to generate electricity.

The visit by Sudan's Bashir, who has travelled to African countries since the International Criminal Court (ICC) issued the arrest warrant against him in March for war crimes in Darfur, puts NATO member Turkey in an awkward position, but a Turkish Foreign Ministry official said there were no plans to arrest him.

"We have invited Bashir as one of the heads of state to the meeting and he will be treated as one," the official said.

Turkey, which has deepened commercial ties with Sudan, has not ratified the 2002 Rome Statute that established the ICC, but is under pressure to do so to meet European Union standards.

WESTERN WORRIES

The attendance of Palestinian Prime Minister Salam Fayyad and Syria's President Bashar al-Assad might also add weight to the summit of the OIC, which has little political power.

Palestinian President Mahmoud Abbas said on Thursday he did not wish to run for re-election in January, voicing disappointment at Washington's "favouring" of Israel in arguments over re-launching peace talks.

Afghan President Hamid Karzai, in what would be his first trip abroad since his re-election was announced this week following a fraud-marred ballot, is also expected to attend.

Ahmadinejad's visit to Istanbul will follow a state visit last month by Turkish Prime Minister Tayyip Erdogan to Tehran, in which the two countries signed trade and energy deals.

Ankara's growing attachment to Iran has fuelled worries that Turkey, a moderate Muslim democracy and a U.S. ally, is turning its back on Washington and the EU, something it denies.

"Policymakers in the West are getting worried that Turkey's growing ties with Iran -- by lessening that country's sense of isolation -- may frustrate diplomatic efforts to prevent Tehran from building a nuclear bomb," Katinka Barysch, of the Centre for European Reform thinktank, wrote this week.

Erdogan's AK Party government, which has roots in political Islam, has sought to expand Turkey's influence in the Middle East -- a process analysts say has run in parallel with Ankara's frustration at perceived EU misgivings over its membership bid.

During his warmly received trip to Tehran, Erdogan blasted Western powers for treating Iran "unfairly" and said the Islamic republic's nuclear programme was for humanitarian purposes.

Ian Lesser, from the German Marshall Fund of the United States, said that by inviting Ahmadinejad and Bashir, Turkey might deepen perceptions its foreign policy is ambiguous.

"It is an example of the risks that Turkey is running by trying to be too many things in too many places at the same time and without too much discrimination," Lesser said.